Kaplan turbines are used in many hydroelectric installations, and are distinguishable from other types of turbines primarily in that they have variable pitch blades which may be adjusted during operation to obtain maximum operating efficiency from existing conditions of gross headwater level and gate position. It is well known in the art to use a governor to automatically control the gates of the turbine (and thereby the flow of water to the blades) in order to achieve and maintain predetermined setpoint power generation levels, and to use an electronic microprocessor-based 3D cam to position the variable pitch blades in response to the gate position and gross headwater level in order to obtain maximum operating efficiency at the desired power generation level.
A turbine vendor generally provides an initial 3D cam surface (as a function of head and set gate) to a user, installed in the electronic 3D cam. This initial 3D cam surface is developed based on model tests conducted by the vendor under simulated conditions, and therefore, merely constitutes an estimate of what the turbine's actual efficiency profile is expected to be when it is bullt and run in its actual operating environment. If it is desired to refine the initial 3D cam surface to accurately reflect the turbine's true efficiency profile, the turbine can be index tested, and the data collected during the index test used to define a new optimum 3D cam surface (i.e., to program a new memory chip for the 3D cam with the new surface profile). Periodic index testing of the turbine is also desirable in order to update the 3D cam to reflect changes in the turbine or its environment.
It has been conservatively estimated that through index testing of turbines, and the resultant upgrading of turbine 3D cam surfaces, an average 1% increase in turbine operating efficiencies can be achieved. Thus, millions of dollars worth of lost electrical power can be reclaimed by identifying and correcting factors that degrade turbine efficiency. Moreover, index testing provides useful information for identifying and correcting turbine deterioration, minimizing cavitation, optimizing turbine maintenance schedules and modeling operating envelopes for Kaplan turbines. In addition, index test results can be used in larger schemes to optimize aggregate operating efficiency for a number of units. More specifically, maximum efficiency can be realized in facilities that operate several turbines by identifying the generation level (for the existing head) at which maximum efficiency can be achieved for each turbine. Thus, individual units can be operated at their particular efficiency peaks (when power demands from the grid allow operating at less than full output).
Despite the numerous benefits provided by index testing, such tests are often not performed on a turbine at commissioning (i.e., to refine the initial 3D cam), and are only occasionally, if ever, performed on a unit during its lifetime. The reason for this is that the classical index test procedure -- defined in the 1952 Index Method of Testing supplement to PTC-18 (the Power Test Code from the ASME) -- requires extensive manpower (from 4 to 14 people, depending on unit complexity and layout) and interruptions to normal unit service. In addition, classical index test methods cause time-consuming delays due to correlating changes in unit generating level with the power dispatcher, and also due to waiting for water levels to stabilize after flow changes are made.
These deficiencies, which have been a deterrent to greater use of index testing, will be better appreciated from the following simplified description of a classical index test. In a classical index test, the blades are manually positioned at a series of blade tilt angles, the gates are set at several positions for each blade position, and turbine operating parameter measurements are made (manually) at each gate-blade operating point. Since both the blades and gates are being moved independently, different power generation levels and discharge flow rates result at each test point. Consequently, sufficient time has to be allowed for tailwater levels to stabilize after each change in gate and/or blade position, and the changes in generation have to be coordinated with the power dispatcher so that the total power to the grid can be held constant.